I think filtering is a very grey area. Different people can read the road in different ways, eg,

Technically, you could have been in the wrong - The car has started to move left from the outside lane, (presumably) to the inside lane (without indication), yet you have started an "undertake" move on him, causing him to stop!

But, if the car was moving from the inside lane to the outside lane, he has failed to spot you overtaking him - then it's a different ball game that's more in your favour!